Hopes for a grand bipartisan debt limit deal took a big hit Tuesday after Sen. Tom Coburn pulled out of the “gang of six” talks.

“I’m not planning on participating at this time,” the Oklahoma Republican told reporters, citing an impasse on entitlement spending.

Fellow GOP gang of six member Sen. Saxby Chambliss (Ga.) said the group would not go on as a “gang of five.”

“No, we won’t,” he said.

But Senate Majority Whip Dick Durbin, who also belongs to the group, said that the remaining five members would meet Wednesday and that he hopes they will continue their work even if Coburn does not return.

“He’s made a valuable contribution, but we have worked so long and so hard, I hope that we can finish this and present it to the Senate,” the Illinois Democrat said.

Chambliss expressed hope that Coburn would eventually return to the group and that something could still be worked out.

“We’re going to continue the effort. I would hope that eventually we’ll still as a group of six be able to come to some long-term resolution of the issue, but that’s not going to happen short term,” Chambliss said.

The group has been working for months on a $4 trillion package of deficit reductions based on last year’s fiscal commission plan, but progress had come to a halt.

“You come to a point in time where people can’t give or won’t,” Coburn said.

He said he would return to the talks if things change. Coburn added that he didn’t think there was enough reform of entitlements, such as Medicare and Social Security.

“We have to do what’s best for this country regardless of who it costs or what, but it’s got to be balanced,” he said.

Coburn declined to go into detail because there was still a chance the talks could be revived.

But one source close to the talks said the break occurred after Coburn demanded an additional $130 billion in Medicare cuts over the next decade from current beneficiaries. That proposal goes beyond what was included in the president’s fiscal commission plan, on which the group was basing its talks.

“He is asking for deep Medicare cuts beyond what the fiscal commission proposed and beyond even Paul Ryan’s [R-Wis.] proposal,” the source said. “That is just not going to happen.”

Still, Coburn remained committed to raising federal revenues as part of any deal. The group has been working on a proposal that would lead to lower tax rates overall but would bring in more revenue by eliminating some tax subsidies and credits.

The willingness of Coburn and the other Republican members of the gang of six —&nbsp; Chambliss and Mike Crapo (Idaho) — to consider increasing revenue has made them a target of Grover Norquist, president of Americans for Tax Reform. It also has put them at odds with GOP leadership, which has repeatedly rejected any proposals for additional tax revenue, even if they are is accompanied by lower tax rates.

But the group has appeared to lack support from leaders of both parties. Senate Minority Leader Mitch McConnell (R-Ky.) dismissed the group’s talks in recent weeks, saying repeatedly that the bipartisan negotiations led by Vice President Joseph Biden were more likely to lead to a deal. Biden’s group has agreed so far on about $150 billion in spending cuts but still has a long way to go, said Minority Whip Jon Kyl (Ariz.), whom McConnell tapped to be the Senate GOP’s lead negotiator with Biden.

Nonetheless, lawmakers on both sides of the aisle had repeatedly put their hopes in the group, which also includes Budget Chairman Kent Conrad (D-N.D.) and Sen. Mark Warner (D-Va.). Earlier this year, 64 Senators — 32 from each party — signed a letter to President Barack Obama praising the group.

Coburn’s exit, meanwhile, came as Senate Democrats appeared to be in no rush to pass a budget of their own.

Conrad still has not lined up the votes he needs on a Democrat-only budget resolution. His efforts have been caught between moderates worried about taking tough votes and liberals demanding modest spending cuts.

Given that Conrad’s budget blueprint will likely be tossed in the trash by the House as soon as the Senate passes it, many Democrats feel the political value of passing one remains questionable: Democrats would get to say they passed a budget, unlike the previous year, but they would give Republicans a chance to take political shots.

In the meantime, Senate Majority Leader Harry Reid (D-Nev.) has been content to hold votes on oil company taxes and judicial appointments. And Reid said Tuesday that he would like to vote next week on House Budget Chairman Paul Ryan’s budget, which Democrats are happy to vote against.

But their own budget is another matter.

“There are a lot of good ideas out there and there’s not a pressing need to commit to one,” a senior Democratic aide said.

Conrad hasn’t given up yet, but he has little margin to spare.

His job appeared to get tougher Tuesday when Sen. Ben Nelson (D-Neb.), who is up for re-election next year, said he wouldn’t vote for a budget that includes tax hikes.

“I’m only focused on cuts, not on raising taxes,” he said. “If we start getting our attention over to raising taxes, I can assure you that many of my colleagues are going to be less interested in cuts.”

Conrad’s draft budget would increase taxes on upper-income Americans — something that is supported by the vast majority of Democrats. But Conrad can only lose three votes in a 53-47 Senate.

“Any successful plan to reduce the deficit and eliminate our debt is going to have to involve revenue increases and spending reductions,” the Louisiana lawmaker said. “Sen. Conrad’s plan is very interesting to me because it includes all of the above.”

Landrieu said Democrats should move ahead on the budget. “Leadership is not just saying no; leadership is about finding compromise,” she said.

Other moderate Democrats up in 2012 — Sens. Claire McCaskill (Mo.) and Joe Manchin (W.Va.) — also said Tuesday they could support a tax on millionaires in the Democratic budget.

Conrad is seeking to cut the deficit by $4 trillion over 10 years, but his plan relies much more on tax hikes than the group’s plan.

Key factions in the Democratic caucus, however, have yet to rally behind any single plan, which Reid alluded to while speaking to reporters after Tuesday’s lunch.

“We have a number of moving targets, and [there’s] nothing wrong with that,” the Nevada Democrat said, referencing the gang of six, Conrad’s budget and the Biden talks.

“Every one of the people involved in those meetings say we’re making progress,” Reid said.

Coburn pulled out of the group shortly thereafter.

Jessica Brady contributed to this report.

Editor's Note:

This article updates the print version to include Sen. Dick Durbin’s comments that the remaining five members of the “gang of six” will meet Wednesday.